A Ti:Sapphire laser complete with 2nd and 3rd harmonic units has been
received and installed at the off-line ion source test facility 2
(ISTF-2). This laser is the first of three Ti:Sapphire lasers that we
will need for a RILIS. It is manufactured by Photonics Industries
International, Inc. and its prototype was first tested at ISTF-2 in
2006. Pumped by 18 W of pulsed 532 nm laser at 10 kHz from a Nd:YAG
pump laser, it can delivery about 2 W fundamental peak power near 800
nm and more than 300 mW and 100 mW peak power in frequency doubled and
tripled outputs, respectively. It is also continuously tunable from
700 nm to 960 nm, with typical linewidths of 1-3 GHz. Fig.7-1 shows a
photo of the Ti:Sapphire laser together with the Nd:YAG pump laser.

Figure 7-1: The new Ti:Sapphire laser and its pump laser. Also shown
are two additional Ti:Sapphire lasers from Mainz University, which are
also pumped by the Nd:YAG laser.

In a RILIS, a particular isotope can be selectively ionized by laser
radiation via stepwise atomic resonant excitations followed by
ionization in the last transition. In order to yield a useful RIB
current, maximized ionization efficiency is required. The RILIS
efficiency is often limited by insufficient laser power to saturate
the last ionization step. It is thus important to find schemes that
lead to ionizing an excited atom resonantly through an autoionization
(AI) or Rydberg state, which are much more efficient than non-resonant
transitions to the continuum. Therefore, an important focus is to
develop the most efficient ionization schemes for a range of elements
of interest.

Ionization schemes for four new elements - Co, Ho, Tb
and Dy - have been investigated in recent experiments conducted at
ISTF-2 in collaboration with the LARISSA group led by Klaus Wendt of
the University of Mainz and, for the first time, the TRIUMF ISAC laser
ion source group led by Jens Lassen. The experiments were performed
with our hot-cavity laser ion source, our new Ti:Sapphire laser, and
two additional Ti:Sapphire lasers with harmonic generation units from
the University of Mainz, which are also shown in Fig.7-1. Since there
were no known resonant ionization schemes for the four elements using
Ti:Sapphire lasers, searches for high lying Rydberg and AI states in
these elements were necessary. With the new Photonics Ti:Sapphire
laser, we were able to study the atomic spectroscopy of each element
over a wide wavelength range. The Photonics Ti:Sapphire laser's
continuous tunability proved to be extremely useful for such
studies. Consequently, many AI states were observed for each element,
most of them for the first time. Three-photon resonant ionization
through AI states was achieved for Co. For Ho, Tb, and Dy, two-photon
and three-photon ionization schemes were studied. Although no Rydberg
states that led to resonant ionization were observed, many AI states
were found in all three actinides. Fig. 7-2 shows some of the resonant
ionization schemes established for these elements. Analysis of the
experimental atomic spectroscopic data is in progress.

Figure 7-2:
Resonant ionization schemes for Co, Ho, Dy, and Tb.

The ionization
efficiency for Co and Ho has been measured using liquid samples that
contained a known amount of the neutral atoms. Using the
three-photon resonant ionization schemes shown in Fig.7-2, the overall
ionization efficiency was found to be more than 20% for Co and about
40% for Ho. The 40% efficiency for Ho is the highest RILIS
efficiency ever reported for any element.